With development of communication technology, cognitive radio attracts more and more attention. Cognitive radio is characterized by flexibility, intelligence, and re-configurability. By sensing external environment and learning from the environment through an artificial intelligence technology, the cognitive radio changes certain operation parameters (such as transmission power, carrier frequency, and modulation technology, etc.) purposefully in real time, and makes the internal state adaptable to the statistical change of received radio signals, thereby implementing highly reliable communication anytime anywhere and making efficient use of limited radio spectrum resources in a heterogeneous network environment. The essence of the cognitive radio is to implement dynamic spectrum allocation and spectrum sharing through spectrum sensing and the intelligent learning capability of the system.
To manage and allocate spectra to different systems dynamically, researchers put forward a concept of cognitive pilot channel (CPC, Cognitive Pilot Channel). It is very time-consuming and power-consuming to obtain radio environment information by only sensing and sweeping the spectra one by one in the frequency band from 400 MHz to 6 GHz. The CPC can manage and allocate the spectra in real time, and a terminal can obtain information on use of the radio spectrum by reading the CPC channel.
A Long Term Evolution (LTE, long term evolution) system can share a spectrum with TV channels or a GSM system, and so on, and different LTE operators can also share the spectrum. An LTE transmitting terminal is a data modulation apparatus for modulating and sending data, and an LTE receiving terminal is a data demodulation apparatus for receiving and demodulating data. For example, FIG. 1 is a schematic diagram of sharing a spectrum between the LTE and the TV channel, in which a busy frequency band in use, whose bandwidth is 8 MHZ, exists between two idle frequency bands. The frequency band on the left side of FIG. 1 has a bandwidth of 8 MHZ. The LTE system uses only frequency bands whose bandwidth is 5a MHZ (a is an integer) such as 5 MHZ, 10 MHZ, 15 MHZ, and so on. Therefore, the LTE system is unable to make full use of a frequency band whose bandwidth is 8 MHZ, and 2 MHZ or (2+5a) MHZ need to be added to the 8 MHZ to make up a 10 MHZ frequency band so that the frequency band can be made full use of by the LTE system.
In the conventional art, as a spectrum management apparatus, the CPC network senses the use of spectrum in a radio scenario, and sends the spectrum usage information to the transmitting terminal and the receiving terminal of the LTE system. The spectrum usage information includes specific locations and bandwidths of the idle frequency bands and the busy frequency bands among the frequency bands. The LTE transmitting terminal receives the spectrum usage information and converts the data, and then performs windowing and filtering and sends the processed data out through an idle frequency band according to the spectrum usage information of the CPC network; the LTE receiving terminal receives and demodulates the data. Artisans find that when the LTE system shares the spectrum, if the data is modulated through a traditional filtering method, discontinuous frequency bands generate considerable out-of-band emission. Therefore, artisans propose to pre-filter baseband signals when the LTE transmitting terminal modulates data to suppress out-of-band emission of discontinuous bands.
In researching and practicing the conventional art, the inventor finds that the LTE transmitting terminal pre-filters the baseband signals, but the pre-filtering operation is not notified to the LTE receiving terminal; with the receiving terminal being unaware of the pre-filtering operation, the demodulation error is considerable.